Leo was a lying and manipulative control freak scumbag who totally deserved to be rubbed out by Frank at the end. Leo was planning on making Frank work for him until he burnt himself out, so Frank had no choice but to kill Leo at the end.
You've seen Guy Standeven in something because the man was in everything.

Leo was scum. Just because he said, doesn't make it true - it's a movie. Take what evidence is given to you.
I don't like violence (in real-life or in movies) but I was so glad when he was killed, without being able to even lay a finger on James Caan.

Hahahaha, you are so right.
Thumbs Up, Thumbs Down and a Wagging Finger of Shame

OP is going to keep making these kind of posts until he finds someone who agrees with him, but he never will because everyone else in the world gets it.

I think that Frank fell for Leo presenting himself as a father. Leo may have known enough about Frank to do that.

Once Leo got his hooks into Frank, he knew there was no way out. Leo said himself he was going to work Frank to death and he would have gotten pain less and less until he was a slave. Leo told him straight up that he could quit anytime, but didn't mean it. How could you expect honesty for such a slimy crook? If you lay down with dogs you're going to get fleas. Frank may have been a great thief, but otherwise he wasn't very bright.

Leo definitely took care of Frank, but he lied during the negotiation of the deal. Frank made it clear he wanted out after that last score. Frank should have listened to his gut and avoided Leo.